The present invention relates to techniques for picking up materials, namely techniques that enable a material to be picked up, i.e., gripped, by acting on the surface thereof.
The invention has been developed with particular attention paid to its possible application to the picking-up of web material wound in reels, above all in plants and systems for the fabrication of hygienic and sanitary products, such as nappies, diapers, incontinence pads, sanitary pads, etc. Reference to this specific field of application must not, however, be interpreted as in any way limiting the scope of the invention, which is altogether general and which can extend, for example, in a particularly advantageous way, to plants and systems for automatic packaging.
In the applicational contexts referred to above, there is generally the need to pick up web materials from reels on which the said materials are wound.
The corresponding systems are designed to operate at increasingly higher rates, and consequently the speed of unreeling of the web material tends to increase more and more. In order to ensure continuity of operation, there thus arises the need to perform as rapidly and efficiently as possible the change-over operation, understood as the operation aimed at connecting the tail part or trailing end of a web that is reeled off from a reel that is in the process of running out to a head part or free leading end of a xe2x80x9cnewxe2x80x9d web available on a replacement reel. The above operation must be performed as fast as possible and in such a way that in practice it will be unnoticed by the equipment downstream.
The technical problems involved in meeting the aforesaid need basically fall into two main categories.
One first category is linked to the construction of the jointing or splicing equipment proper, commonly referred to as xe2x80x9csplicerxe2x80x9d.
Another categoryxe2x80x94closely linked to the previous onexe2x80x94regards the construction of accumulation devices that can reel onto themselves a certain amount of web which is then to be fed to the processing equipment located downstream while the splicing operation is in progress, in static conditions or in conditions of marked deceleraton of the movement of advance of the web.
The corresponding prior art is considerably extensive, as is documented by the vast amount of literature, including patent literature, devoted to the subject. Purely as a reference, the document EP-A-1 013 585 may be cited, which illustrates in detail an accumulation device of the type referred to above.
The invention specifically tackles a problem in a way so to speak complementary to the problems seen previously, namely that of enabling picking-up, i.e., gripping, in a secure and reliable way of a sheet material, the aim being, for example, to enable formation, on a reel of web material, of a free end of the web that can be used for the aforesaid splicing operation (the so-called xe2x80x9cflying changexe2x80x9d) in the terms previously described.
In tackling the above-mentioned problem, numerous factors must be taken into account.
In the first place, the characteristics of the materials that are to be gripped may differ a great deal. Even if we limit our considerations to the sector of hygienic and sanitary articles, the range of materials is extremely wide: from plastic materials, which frequently have a large number of holes or openings (for instance, the perforated film normally used for making the so-called xe2x80x9ctopsheetsxe2x80x9d of sanitary pads or diapers), to substantially continuous types of film with surfaces that may be either completely smooth or with a certain degree of surface roughness or microroughness (for example, the types of film used for making the backsheets of the articles referred to above), or yet again to materials having an intrinsically porous nature (such as certain non-woven fabrics or absorbent materials in sheets), and to yet other different materials. It must also be considered that these are frequently materials which are on the whole delicate and hence cannot stand up to high tensile stresses.
For materials wound in reels it is important to take into account factors linked to the characteristics of the reel: diameter, length measured in the axial direction, any possible eccentricity both as regards the path of winding about the core of the reel and as regards any possible warping of the periphery of the reel when the latter is made to turn about its own axis.
There is moreover the specific problem linked to how the free end or flap of the web is fixed to the body of the reel, i.e., whether with a stretch of adhesive tape, possibly applied by hand in a position that is not difficult to foresee, or by local bonding, welding, etc. Clearly, the range of possible situations is very wide.
For this reason, even though the operations of splicing and accumulation described previously are today carried out by resorting for the most part to automatic equipment, the operation of locating the free flap of the xe2x80x9cnewxe2x80x9d reel which is to be used for a splicing operation, as well the operations of preparing the flap in view of the splicing operation are carried out manually by an operator. The corresponding interventions prove critical both on account of the frequency with which they are required (splicing operations between consecutive webs tend in fact to follow one another at ever shorter intervals as the speed of operation of the equipment increases), and on account of the possible consequences of any errors or imprecisions (a delay in preparing the free flap in view of the splicing operation or any error in the preparation of the said flap results in fact, almost inevitably, in the need to stop the equipment).
Consequently, the purpose of the present invention is to provide a solution such as may enable the said operation of picking up and detecting the free end in an altogether automatic way.
In more general terms still, the present invention tackles the problem of providing for gripping of a material, such as a web or sheet material, in a secure and reliable way when the surface characteristics of said material (for instance the fact that it is a perforated or porous material, or else there is the presence of surface roughness) make it difficult to ensure a precise and definite grip on the material, using a device operating by suction, i.e., with a pressure value that is below atmospheric pressure.
According to the present invention, the above purpose is achieved thanks to a process having the characteristics specifically referred to in the ensuing claims. The invention also relates to the corresponding device.